1. Field of the Invention
This invention relates generally to an electronically controlled, high resolution light source, and more particularly, to a high resolution light source formed from a thin film electroluminescent edge emitter assembly sealed within a protective package.
2. Background Information
It is well known that an electroluminescent device generally, and particularly a thin film electroluminescent edge emitting device, may be utilized to provide an electronically controlled, high resolution light source. One such type of application is disclosed in U.S. Pat. No. 4,535,341 to Kun et al. which is assigned to the assignee of the present invention. This patent discloses a thin film electroluminescent line array emitter structure which includes a first dielectric layer disposed on a common electrode, a second dielectric layer spaced from the first dielectric layer, a phosphor layer interposed between the first and second dielectric layers and an excitation or top electrode disposed on the second dielectric layer. At least one of the electrodes, for example, the excitation or top electrode, is segmented to form a plurality of individual control electrodes. The plurality of individual control electrodes in combination with the remaining structure define a plurality of individual light-emitting pixels.
Another example of a device which utilizes an electroluminescent light-emitting unit as a light source is illustrated in U.S. Pat. No. 4,734,723. This patent discloses an electrophotographic printer which includes an optical head formed from a plurality of electroluminescent devices positioned along one edge of a substrate. A plurality of light waveguide strips are also formed on the substrate in association with the electroluminescent devices, and the waveguide strips serve to transmit the light from the electroluminescent devices to the other edge of the substrate which is brought into a face-to-face relationship with the printer photoreceptor.
Japanese Laid-Open Patent Application KoKi No. 63-91998 discloses an EL luminescent edge emitter array in which the upper side metallic electrode wraps around the reflecting end surface of the luminescent layer. Each of the EL elements in the array is surrounded by an insulating film whose refractive index is lower than that of the EL layer. The array further includes a discharge prevention area between the bottom electrode and the reflecting end of the top metallic electrode.
Although the prior art disclose thin film electroluminescent edge emitter devices of various form, none of these structures includes an integral housing or packaging assembly operable to protect the device itself from damage due to moisture or other harmful contaminants. It is apparent that if an edge emitter is to be used commercially as a high resolution light source, then the edge emitter itself must be isolated from these contaminants in order to provide extended, maintenance-free service.
Therefore, there is a need for a thin film electroluminescent edge emitter assembly sealed within an integral housing or packaging assembly. The packaging assembly is operable to provide a contaminant-free environment for the edge emitter. At least one wall of the packaging assembly is formed from a translucent material to permit the light energy emitted by the edge emitter to pass through the translucent wall to the exterior of the packaging assembly. In addition, the packaging assembly itself should be of compact design to permit the edge emitter which it houses to be advantageously used as a high resolution light source in devices such as electrophotographic-type imaging stations or printers.